1. Field of the Invention
The present invention is directed to an electromagnetic pressure pulse source for generating focused pressure pulses, of the type having an electrically conductive membrane which is rapidly displaced by means of a coil system.
2. Description of the Prior Art
Electromagnetic pressure pulse sources having a membrane driven by a coil system as described, for example, in U.S. Pat. No. 4,674,505, are used for medical purposes in the treatment of calculosis, pathological bone conditions and pathological tissue changes. Such a pressure pulse source is normally applied to the body surface of the patient by means of a flexible coupling pillow, filled with a liquid medium for acoustic coupling. As a consequence of the flexibility of the coupling pillow, the spacing of the pressure pulse source from the body surface can be set, while maintaining contact between the coupling pillow and the body surface, so that the focus of the pressure pulses lies in the zone to be treated. The zone to be treated will be at a different depth below the surface dependent on the individual treatment case. Because the spacing of the focus from the body surface can be varied only to a slight extent in this manner, a number of proposals have been suggested to alleviate this situation. For pressure pulse sources wherein the pressure pulses are focused by an acoustic lens, for example, it is proposed in German OS 37 35 993 to provide two such acoustic lenses with variable spacing between the lenses to displace the focus, or alternatively to provide a lens having a variable focal length in the form of a liquid lens (vario lens).
All solutions heretofore proposed for displacing the focus have significant disadvantages associated therewith. In the aforementioned technique of displacing the focus by adjusting the distance of the pressure pulse source from the body surface of the patient, problems arise if the treatment zone lies immediately under the body surface, because of the small entry area for the pressure pulses which is then available. This results in the skin of the patient, which is sensitive to pain, experiencing high stress, such that hematoma can even occur. In the case of pressure pulse sources having an ultrasound B-scan applicator arranged in a central bore of the pressure pulse source for locating purposes, the B-scan applicator must be retracted if the zone to be treated lies close to the body surface, since it would otherwise be in the propagation path of the pressure pulses. This means that no ultrasound images, or only poor ultrasound images, can be produced while charging the patient with pressure pulses. Additionally, the necessary mechanism for adjusting the pressure pulse source, and possibly the B-scan applicator as well, involves considerable outlay.
The aforementioned pressure pulse source disclosed German OS 37 35 993 also has the above disadvantages, because although the mechanism for adjusting the pressure pulse source can be eliminated, a mechanism must nonetheless be provided for adjusting one of the lenses. This disadvantage can be avoided by using a vario lens for displacing the focus, however, a vario lens permits the focus to be displaced only slightly, and additionally involves a not inconsiderable design outlay and space requirement.